In general, drip coffee which is made by dripping boiling water over ground coffee, which is prepared in a filtering device after being roasted and ground, or an espresso which is brewed by passing boiling water under high pressure through finely ground and compressed coffee beans is regularly used.
In recent years, many people increasingly prefer Dutch coffee which is extracted using normal water or cold water for a long time, about 3-24 hours.
In addition, an extracted liquid of Dutch coffee ages with time and has more distinctive flavor and aroma. In addition, since Dutch coffee is extracted using normal water, it contains less caffeine than drip coffee or an espresso which is extracted in boiling water, and has a deep, soft flavor.
In addition, since the Dutch coffee can be stored for a long time and the aroma and flavor of coffee which may dissipate due to boiling water may be extracted as they are, the Dutch coffee can provide the rich aroma of coffee and distinctive flavors that hot coffee does not provide, such as a bitter flavor, a sour flavor, and a sweet flavor.
A related-art Dutch coffee extraction apparatus controls a speed of extraction of Dutch coffee and an amount of coffee to be extracted using a valve. However, the valve should be manually opened and closed by a user to control the speed of extraction and the amount of coffee to be extracted
In addition, in order to control the speed of extraction and the amount of coffee to be extracted after the valve is opened, the valve is minutely controlled. However, since the Dutch coffee is extracted for a long time, it is common that the coffee is extracted at the same speed and by the same amount from the time the Dutch coffee is initially extracted until the time the extraction is completed.
Therefore, the related-art Dutch coffee extraction apparatus may fail to control the speed of brewing of an extracted liquid which is extracted while passing through a filtering container, and there may be a problem that the flavor and aroma of the extracted liquid of the Dutch coffee are spoiled and quality deteriorates. In addition, since ground coffee does not stay for as much time as desired, the concentration of the extracted liquid becomes low, and accordingly, there is a problem that the production of products decreases.
In addition, in a process in which water in a water tank drops down to the filtering container which contains ground coffee powder, water may not drop down to the whole coffee powder and may flow down along the wall of the filtering container. Therefore, the water may be brought into contact with only the coffee powder existing around the circumference of the filtering container. As a result, Dutch coffee of a constant concentration may not be extracted and thus Dutch coffee of a low concentration may be extracted.
In addition, there may be inconvenience that the user should stop continuously extracting the Dutch coffee in order to prevent water from being supplied only to the circumference of the filtering container, and should shake coffee powder contained in the filtering container in order to change the positions of the coffee powder. Since the user should stop continuously extracting coffee, the quality of extracted coffee unavoidably deteriorates.
In addition, since the aroma generated when the Dutch coffee is extracted is not collected in an extracted liquid storage container and the aroma of the Dutch coffee dissipates, the user may not feel the rich aroma of the Dutch coffee when drinking it and also may not feel the taste due to the reduced aroma.
In addition, the related-art apparatus may have a filter installed in a narrow extraction pipe which is disposed under the filtering container in order to convey the extracted Dutch coffee to the extracted liquid storage container, and it is common that Dutch coffee is contained on the upper portion of the filter.
However, since coffee powder is contained in the narrow extraction pipe, the coffee powder may agglomerate when water is supplied to the coffee powder, and thus, the extracted liquid may not be extracted to an extracted liquid conveying means at the right time and may stay in the filtering container with the coffee powder for a long time. To this end, a maximum value of an action of extracting ingredients of coffee powder is exceeded and there is a problem that a bitter flavor of coffee powder having water solubility is extracted.
In addition, since water stays in coffee powder for more than a predetermined time, oil may be produced from the coffee powder and coffee may taste like oil. Extracting may excessively be performed and thus bad ingredients may be extracted.
In addition, since the related-art Dutch coffee extraction apparatus has the single filtering container installed under the water tank, and has a single extraction container installed under the single filtering container, and should continuously extract for about 3-24 hours, it is common that a large amount of coffee cannot be extracted at one time.
Therefore, there is a problem that an amount of Dutch coffee extracted within a predetermined time is limited and thus more Dutch coffee cannot be provided to consumers.
In addition, since many Dutch coffee extraction apparatuses should be provided in order to extract more Dutch coffee, there is a problem that it cost much to buy Dutch coffee extraction apparatuses.